I did the method where you start from square one. Treat the hand you want to train as a baby’s hand. Start easy and build up slowly.

Do not force or overwork yourself! Do baby steps. Everyone will have their own pace. But please be gentle to your hand. Especially the wrist, it’s fragile.

Start using the arm you're training more in your daily life. Opening doors, opening cans, bottles, stirring sauce, brushing teeth, holding items etc. You build up the usage and level up to more activities as you get the hang of it. (I can now use a KNIFE well to cut carrots! Left hand in table tennis, heck yeah!).

Start with doing it only a few times a day or stuff that last 10 minutes until you get a better grip.

Every day I do a page of writing (be just letters, or numbers or words). Eventually I added another page of drawing circles and lines to get used to how I grip my pen. 

When I felt I had better control and I was able to last longer without my hand getting tired. I added a 30 min of gesture drawings to the list.

So I try to make sure I do at least half an hour of activities with my non-dominant hand. And then if I have time in my day, I do a bit more of what I can. In the start my hand would get very tired fast, that I was barely able to last 1 hour without my arm dying from the death grip I had back then and the only way I was able to hold my pen still (I mean it would still shake a lot).

Now lasting over an hour is easy breezy and I can hold the pen with the same pressure as my dominant hand.

Note: you're not just training your hand. But your whole body. To get used to how it supports the arm and how that supports the wrist, supporting the hand, to the fingers, you get the gist. You are rewiring a bunch of stuff in your brain.

I don't worry about being accurate yet. It's more to get the arm muscle built up and trained to the different motions. 

When I feel like I’ve improved in an area, I would give myself something new to get used to (staying on the lines of the page, smaller writing, using a nib pen etc).

Now the weekly art. It started as a way to keep me on track (as before this, I know I tried to train my non-dominant hand a few times and didn't last longer than like a month) and posting online gave me the pressure to stay on track. And it’s a good way to see my progress and the control I had on drawing over time.

Which resulted in drawing Coran every week for 100 weeks. I liked drawing him anyway so it was a win win. (I am going to admit, honestly I kind of miss drawing Coran like every week. Also this reminds me i need to post the video of the 100 left Coran pieces /:P).

Same thing with everything else, it was building it up over time. I would do batches and switch around to different styles and mediums to get used to. When I’ve felt myself improving in an area, I would then challenge myself (using ink pens only, drawing on tablet, on larger paper etc). 

And with every new thing I’ve tried, it starts with being very difficult to do. But it’s just something to practice on.

For me the most important thing was not to fall completely off track.

I do allow myself to lag behind a little bit. Because sometimes life happens. Either missing the weekly art pieces, or cut down to only doing a page of writing that day. Or skip a day or two.

Perhaps it feels my left hand needs a rest (maybe because I was helping with moving boxes or that certain weekly art I worked a bit too long on than I’m used to at that point and it needs to recover).

I do try to at least do some type of activity with my left hand on those types of days (be it just stirring my tea). Then I would work on catching up (usually only for the weekly art pieces I miss). Posting online helped me keep track of this.

It’s all about building up your arm, but make sure you are kind to it as you do. Health comes first, that's the top rule. Mix something you enjoy with the training. Always adjust the training to suit you best. Find your own pace. It might be you find completely different methods that help you in this journey.

For me it’s for sure and has been a very long journey. There’s are still a lot areas I have difficulty with and needs more practise.

But seeing the actually progress I’ve made over the years (be it with my art, the old pages I’ve kept with my writings, gesture drawings or the notes on how it felt using my arm at different stages).

Makes me happy (as I have issues with my dominant arm for awhile). 

It feels nice~

Anywho,

Best of luck :D